Structures and Vibrational Frequencies of Pure Halocarbon Clusters, and Mixed Clusters with Water

Principal Investigator

Gad Fischer

Chemistry

The Faculties

The adverse environmental effects of the halocarbons
are well documented. Not only are they destructive of
the stratospheric ozone layer but they are also
powerful greenhouse gases. Although considerable data on
the infrared absorption by these molecules has been
reported recently, little is known about the role played by
dimers and larger clusters of these molecules, and
their concentrations in the atmosphere. The low
temperatures encountered at high altitudes favour the formation
of clusters.

Co-Investigators

Xiaolin Cao

Chemistry

The Faculties

Projects

u54 - PC

What are the results to date and the future of the work?

The initial approach to this project involved characterization of the monomer species of
the perfluoro cycloalkanes. High level ab initio calculations, (HF/6-31G*, MP2/6-31G* and
B3LYP/6-31G*), on the ground state optimized geometry and force field have been completed
for perfluorocyclobutane. Barrier heights to the ring-puckering motion have been determined
from molecular orbital calculations, and together with the calculated puckering vibrational
frequency have been used to model the infrared spectrum with a quadratic-quartic potential. An
explanation has been obtained for the lack of puckering structure in the infrared spectrum.
Calculations, but at a lower level, have yet to be undertaken for perfluorocyclohexane, and for the
cluster molecules. A sample calculation on a dimer molecule of purine at the HF/6-31G* and
B3LYP/6-31G* levels proved successful.

What computational techniques are used?

The calculations were carried out for the electronic ground state with the GAUSSIAN
molecular orbital programs: HF, MP2, and B3LYP all with the 6-31G* basis. Optimized geometries
and vibrational frequencies were determined under two different symmetry constraints.